1. Field of the Invention
The invention relates to a driver imaging apparatus and a driver imaging method for capturing an image of a driver in a vehicle from the front.
2. Description of the Related Art
Systems are under development which capture an image of a driver driving a vehicle and monitor the state of the driver using the captured image. For example, a camera for capturing an image of the driver from the front is arranged near a steering wheel of the vehicle and the state of the driver is analyzed using the image captured by the camera.
Japanese Patent Application Publication No. 2004-192345, for example, describes a driver state detecting apparatus which determines the degree to which the eyes of the driver are open (hereinafter also referred to as “eye opening degree”) and the direction in which the driver is gazing (i.e., hereinafter also referred to as “direction of gaze”) using an image of the driver. The driver state detecting apparatus described in that publication detects a coordinate value of the eyes of the driver from the image. Then the driver state detecting apparatus determines the direction of gaze of the driver or the degree to which the eyes of the driver are open to determine whether the driver is inattentive or nodding off.
However, when capturing an image of the driver in the vehicle from the front, light from outside the vehicle may produce a shadow around the eyes of the driver, causing that area to appear dark, and thus lack contrast, in the image, i.e., resulting in a dark (i.e., underexposed) image. In this case, the degree to which the eyes of the driver are open and the position of the eyes are unable to be detected so it is difficult to determine the degree to which the eyes of the driver are open or the direction of gaze of the driver.
To prevent this, it is possible to increase the amount of exposure (simply referred to as “exposure” in this specification) when capturing the image of the driver (e.g., increase the electronic shutter time) so as to increase the amount of light on the shadowed portion in order to prevent that portion from being underexposed. However, when the exposure is determined using the area near the eyes of the driver that are in a shadow as the reference, an image in which the area near the eyes is light is able to be obtained but contrast in other light portions such as the outline of the face of the driver is lost (i.e., overexposed). As a result, processing using the image of that light portion is unable to be performed.